Low phase-noise oscillators are important in radio frequency (RF) communication systems and radar systems for generating reference signals. Phase-noise refers to the random phase instability of a signal and may result in a frequency variation in the signal that may appear as energy at frequencies other than the carrier frequency. Close-in phase-noise generally refers to phase-noise that appears at frequencies close to the carrier frequency (e.g., about 5 to 10 kHz).
In the case of radar systems, close-in phase-noise may make it difficult for a radar receiver to detect low-Doppler radar signals or a Doppler-shifted signal close to a pulse-repetition-frequency (PRF) line, or close to a pulse-repetition frequency (PRF) (e.g., a rate at which radar pulses may be transmitted). Sometimes, the PRF spectrum lines may create areas that the radar system must mask out, creating detection holes. Phase-noise may make these detection holes wider. Also in the case of radar systems, close-in phase-noise may also make it difficult for a radar receiver to detect small target returns close to clutter, and in some cases, may make it difficult to detect very large target returns. In the case of RF communication systems, close in phase-noise may make it difficult for a receiver to properly down-convert and/or demodulate received signals to produce accurate data signals.
Thus, there are general needs for an improved oscillator and method of generating an oscillation frequency. There are also needs for a low-phase-noise oscillator and method. There are also needs for a method and oscillator with improved cancellation of close-in phase-noise. There are also needs for a method and oscillator that provides a low phase-noise reference signal suitable for radar and RF communication systems. There are also needs for a method and oscillator that help control phase-noise in a receiver. There are also needs for a radar system that can detect small target returns close to clutter.